Ionic conductivity across the disorder–order phase transition in the SmO1.5–CeO2 system

Samples of SmxCe1 − xO2 − δ (0.05 ≤ x ≤ 0.55) were prepared by solid-state reactions and the disorder–order phase transition and grain ionic conductivity were investigated using XRD and ac impedance spectroscopy technique, respectively. For 0 ≤ x ≤ 0.35 the material has a fluorite structure and gradually stabilizes into a C-type rare-earth structure at 0.40 ≤ x ≤ 0.55 because of oxygen-vacancy ordering. The highest grain ionic conductivity observed is 0.0565(37) S cm−1 at 700 °C for Sm0.20Ce0.80O2 − δ with an associated activation energy (EA) of 0.791(7) eV. The slopes for EA and pre-exponential factor change during phase transition and the conductivity decreases monotonically. Upon comparison of the EA between the SmO1.5–CeO2 and NdO1.5–CeO2 systems, it is seen EA for the SmO1.5–CeO2 system is lower than NdO1.5–CeO2 system at compositions with less than 25% trivalent rare earth element while higher EA is observed for the SmO1.5–CeO2 system at Nd/Sm concentrations above 25%.